Thread breakage detector

ABSTRACT

A NOVEL SEWING MACHINE UPPER THREAD BREAKAGE DETECTOR HAS BEEN PROVIDED WHICH RELIABLY SIGNALS THE FAILURE BY THE SEWING MACHINE TO SEW PROPERLY BECAUSE OF THE UPPER THREAD BREAKAGE. THE THREAD BREAKAGE IS DETECTED DESPITE RELATIVELY HIGH CONTACT RESISTANCE IN THE OPERATING CIRCUIT ATTRIBUTABLE TO VARYING AMOUNTS OF CONTAMINANTS. THE CONTACTS ARE NOT USED DIRECTLY IN OPERATING A RELAY, THE HIGH RESISTANCE CONTACT IS TRANSFORMED TO OPERATE A LOW IMPEDANCE RELAY DRIVE.

United States Patent Inventor Aubrey G. Beazley El Paso, Tex. Appl. No. 795,291 Filed Jan. 30,1969 Patented June 28, 1971 Assignee Farah Manufacturing Company, Inc.

El Paso, Tex.

THREAD BREAKAGE DETECTOR 7 Claims, 4 Drawing Figs.

us. ct. 112/218, 112/219, ZOO/61.18 lnt. Cl B65h 63/02, G08b 21/00 Field of Search 1 12/219,

219(A),218;200/6l.18,61.l3; 139/370 [56] References Cited UNITED STATES PATENTS 2,868 151 l/l959 Winz 112/219 3,425,375 2/1969 Jacobs etal. 112/218 FOREIGN PATENTS 229,683 10/1963 Austria 1 12/219 984,079 2/1965 Great Britain 1 12/219 Primary Examiner-H. Hampton Hunter Attorney-Curtis, Morris, and Safford ABSTRACT: A novel sewing machine upper thread breakage detector has been provided which reliably signals the failure by the sewing machine to sew properly because of the upper thread breakage. The thread breakage is detected despite relatively high contact resistance in the operating circuit attributable to varying amounts of contaminants. The contacts are not used directly in operating a relay; rather, the high resistance contact is transformed to operate a low impedance relay drive.

PATENIED JUN? 81971 e 1 I l R 1.. 3 n MG A w/ TY.

JOB

THREAD BREAKAGE DETECTOR This invention relates to sewing machines and means for controlling the same, more particularly, this invention relates to an improved device for signalling the necessity for stopping a sewing machine upon failure in performance of the upper or needle thread.

For modern high speed sewing machines, various devices suitable for detecting the failure of the upper or needle thread have been proposed. These generally fall into two groups, (a) mechanical means acting upon the thread to sense via some detecting means either electrical or mechanical the absence of the upper thread te nsion,'or (b) electrical means programmed to detect the upper thread failure by establishing an electrical connection detecting the absence of thread tension.

f the first group, devices are known which determine, by being acted upon by the thread itself, the thread tension or absence thereofduringone or more of the eventsmaking up a repeating stitching cycle. Appropriate electrical means programmed to sense thefailure of the mechanical thread detecting means then signal the desired information, i.e., either stopping the sewing machine or notifyingan observer of the failure by the machine to perform-in the conventional manner. A representative device of this type is illustrated in US. Pat. No. 3,029,763.

Of the second group of devices, electrical current interrupters are known which are triggered by thread takeup spring contacting a block. The present invention relates to means detecting upper thread failure classified with the second group of devices.

For better understanding of the devices in the second group and the present invention, reference is made to the accompanying drawings wherein same numerals identify samemembers and wherein:

FIG. 1 shows a conventional threadtensioning device positioned on a sewing machine head and which device is representative of those used on high speedsewing machines;

FIG. 2 illustrates a top'view of the thread tensioning device;

FIG. 3 illustrates a side view of the threadtensioning device; and wherein FIG. 4 illustrates the novel electrical circuit used to detach reliably the thread failure during a high speed sewing operation.

in refei ence to FIG. 1, a thread tensioning device 2 consists of a pair of tension discs 3 and 4 pressed together by a spring 5 on an axis 6 and adaptedto grip a thread 7. When a sewing machine operates at high speed, a thread takeup spring 8 pivots about the axis 6 of the thread tensioner 2. This thread takeup spring 8 is loaded to exert force in clockwise direction until it comes to rest under spring tension against 'a contact block 9. The thread is routed down and up, halfway around the thread tensioner. axis 6 and in the up position through a loop in the thread takeup spring, then back down and around a tension thread guard 11, and thenup through a takeup arm 12 having an eye therefor.

When a sewing machine is running, the clockwise spring tension of the thread takeup spring 8 is overcome by the-tension imparted to the' thread 7 for a period of each complete stitching cycle, thereby causing the thread takeup spring 8- to be pivoted in a counterclockwise direction and away'from'the contact block 9. Hence, the thread takeup spring 8 makes and breaks contact with the contact block once for each stitching or thread feed" cycle. If the needle thread 7 is under tension for a period of each cycle, then it is an exact indication that the needle thread is sewing properly. However, if the needle thread 7 breaks, then the needle thread is no longer undertension, and the thread takeup spring 8 rests continuously against the contact block 9 even though the sewing machinev is running.

Consequently, two distinct events are used to determine the upper thread failure, i.e., (a) the intermittent making and breaking of contact of the spring 8 with contact block 9, and (b) the continuous contact of spring 8 with the contact block 9.

In the past, these events have been used to determine with appropriate electrical means the failure of the thread. Despite the various approaches, the sensing devices designed for use with high speed sewing machines have failed to distinguish reliably the two events. This past failure has been because of lack of suitable electronic means which would work reliably under the changing contaminant levels in the vicinity of the thread tensioner, such as when lint interferes with the sewing operation and accumulates on the thread tensioner or spring.

Thus, if the thread takeup spring 8 and the contact block 9 are used as electrical contacts, lint will rapidly build up on the contact surfaces of the same. Within short time of the operation, the contacts are rendered ineffective for operating a relay circuit. Moreover, these contacts must use a low voltage source for safety, and contact resistance of very low values must be used for energizing relays. Further, contact resistance of varying value builds up due to varying levels of lint contamination associated with materials having different resistivity characteristics.

Still further, the thread tensioner axis 6 in some high speed sewing machines is an axially reciprocating cam follower periodically spreading apart one of the two thread tensioner discs 3 and 4. Consequently, axis 6 carries on its surface some machine oil which has a tendency to attract lint.

Although various approaches have been used to overcome the varying resistance attributable to'the contact resistance, the proposed solutions still have fallen short of a trouble-free and reliable device. Thus, in US. Pat. No. 2,868,151, the proposed circuit requires low voltage and an adjustable resistance for a low pass RC filter. As the high speed sewing progresses, the original contact resistance builds up and the voltage and filter characteristics change because of the introduction of another resistance, placing the capacitor between the two resistances. Hence, the interrupting frequency generated by the stitching operation changes the registered contact frequency, i.e. when lint insulates the contact thereby failing to give a sufficient contact; the high resistance may also change the employed low voltage values and fail to provide sufficient relay drive current. These factors require constant attention to the prior art detecting device which is hardly compatible with high speed sewing machine operations and unattended operation of the same.

It has now been discovered that an improved thread takeup spring contact sensing or detecting device overcomes the prior art detection problems associated with lint contamination while at the same time allowing the detecting device to function reliably over a wide range of operating conditions.

In accordance with the invention, an electronic detection and event programming means are now employed with suitable signalling means either to call to an operator's attention the failure in the thread tension or to stop by appropriate means the sewing machine operation. Basically, the detection means electronically transforms the inlet contaminated high resistance contacts to a low impedance relay drive. The electronic circuit'used for detecting the failure in the upper thread is depicted in FIG. 4. At an initial condition when the machine is not running and the thread takeup spring 8 is making contact with the contact block 9, the indicated solid state device, i.e., transistor 13 is off, as is the indicated solid state device, i.e., transistor 14. The relay 15 is then deenergized.

The relay 16 is connected to energize under conditions when the sewing machine motor clutch (not shown) is actuated. Hence, the signal light 17 can turn on only under certain conditions when the clutch is actuated and not when the clutch is not actuated (or means are provided to deactivate the clutch and retain the signal light under appropriately needed conditions). Thus, relay 16, when energized, establishes the condition that the sewing machine must be running in order for the signal light 17 to be turned on. The relay 15 is energized when the thread takeup spring is rapidly making and breaking contact (on-off condition) with the contact block 9 causing the capacitor 18 to charge rapidly and discharge slowly. This action in capacitor 18 produces a net positive voltage at the solid state device, i.e., at transistor 13 emitter, providing base drive to turn on the solid state device, i.e., transistor 14 and to energize relay 15, thereby keeping the signal light 17 in the off position. If the needle thread 7 were to break while the machine is running, the capacitor 18 will no longer have a charging path because the thread takeup spring 8 will be making continuous contact with the contact block 9 causing thereby transistor 13 to lose base drive.

After a short time of discharge by capacitor 18 of its charge into the base of transistor 14, this will turn transistor 14 off therewith deenergizing relay and turning on the signal light 17 indicating needle thread breakage. Circuit parameters may be adjusted so that when the contact resistance buildup on the thread takeup spring8 because of line or other contaminants reaches the proportions of several thousand ohms this resistance will not affect the circuit operation.

It should be noted that the rapid making and breaking of contact will cause relay [5 to energize, but it will not deenergize when the contacts are momentarily closed as capacitor 18 is holding a charge and providing a base drive to transistor 14 during this period. However, when the contacts are closed due to thread breakage for an abnormally long period of time and while the machine is running, the capacitor 18 will discharge sufficiently so that transistor 14 will lose its base drive turning relay 15 off and the signal light 17 on. It has also been found that if a solenoid valve is substituted for lamp l7 and it is coupled to a pneumatic cylinder these means can operate a sewing machine brake and clutch cylinder and thus signal the failure of the upper thread in the sewing operation.

By way of an example, the following components were found particularly suitable for use in the circuit according to FIG. 4. Of course, it will be understood that the components are given merely by way of an example and are not to be considered as limiting the invention.

Transistor 13 2 N 3704 Transistor l4 2 N 3704 Relay l5 KRP ll DG 24 v. DC (Potter & Brumfleld) Relay l6 KRP ll vDG 24 v. DC (Potter & Brumfield) Signal Lamp 17 N01 327 GB. lamp Capacitor l8 p. uf Resistor 19 lOOK Q Resistor 20 4.7 K O Resistor 21 47 Q. Resistors 22,23 4.7 K 9. Diode 24 l N 5060 Voltage 26 volts When a sewing machine such as depicted in US. Pat. No. 2,938,477 is modified with the above-described device, the failure of the upper needle thread is detected reliably.

lclaim:

1. An upper thread tension detection and sewing machine control arrangement, particularly for determining the failure ofa sewing machine to perform satisfactorily when the upper thread fails to perform in the set manner during a stitching cycle, comprising:

switch means, including a high impedance source of current, operative in a repeating open and closed condition synchronous to a sewing machine stitching cycle for providing an open and closed signal; said switch means being of a varying resistance when closed as a result of contaminants in an operative environment for the sewing machine; and variation of said closed signal due to said varying resistance being negligible due to said high impedance sourcej detection means, connected to the varying resistance switch means for generating a control signal in response to the said detection means generates a signal responsiveto the switch means when said switch means is In a continuous on condition. 2. The upper thread tension detection and sewing machine control arrangement according to claim 1 wherein the detec-.

tion means include a capacitor and two transistors, said capacitor is charged when said switch is in the repeating openclosed condition and said capacitor provides a net voltage for the first transistor to provide a base drive to the second transistor energizing said relay.

3. The upper thread tension detection and sewing machine control arrangement according to claim 1 wherein the detection means include a capacitor and a transistor, said capacitor providing a net positive voltage when said switch is in the repeating open and closed condition in an emitter of the transistor to energize said relay connected to said signal means.

4. The upper thread tension detection and sewing machine control arrangement according to claim 3 and wherein the energized relay keeps the signal means deactivated.

5. The upper thread tension detection and sewing machine control arrangement according to claim 1 wherein the switch means is a thread takeup spring and a contact block and wherein the detection means operates an emitter follower which transforms the high resistance contacts of said takeup spring and contact block into a low impedance for the relay means, and wherein the relay means when said sewing machine is running is in an energized condition and keeps the signal means deactivated when the switch means is in a repeating open and closed condition.

6. An upper thread tension detection switch arrangement for a sewing machine having a thread takeup spring and a contact block which are separated and brought together by the sewing machine's upper thread during normal sewing operation comprising switching means including said spring and block as contacts, one of said contacts being connected to a reference potential, a high impedance connected to the other of said contacts and to a source of potential, said contacts being of varying resistance as a result of contaminants in an operative environment of the sewing machine, and the resistance of said high impedance being several times larger than the largest varying resistance of said contacts when closed for rendering negligible variations in current through said closed contacts as a result of the contact impedance variation.

7 An upper thread tension detection arrangement for a sewing machine having a thread takeup spring and a contact block which are separated and brought together by the sewing machine's upper thread during normal sewing operation, comprising a pair of time constant circuits including a capacitor, said circuits respectively charging and discharging said capacitor said circuits including means providing for different rates of charging and discharging of such capacitor; a switching means including said spring and block as contacts for operating said time constant circuits to alternately charge and discharge said circuits and including high impedance means having a large resistance connected with said contacts for rendering said switching substantially immune from resistance variations across said contacts resulting from an accumulation of contaminants thereon. 

